Symptom: Program does not react correctly on joystick input
or acts as if joystick is moved, though it is not.
Target : C-64
Possible sources of failure
Replace the joystick with a working one. There are two possibilities:
- everything works fine -> old joystick defective or
- problem does still occur, then goto next step.
CIA #1 or EMI filter(s)?
If possible (i.e. if it is socketed), replace the CIA #1 (the
one next to the keyboard connector). For the old boards, this
should fix your problems.
If the CIA is not socketed, you should try to determine which
of the keybard rows or columns are either continuously active
(in this case you usually see one or more characters continuously
printed on the screen) or impossible to access by the keyboard
routine (in this case some keys of the same row or column
are dead). For this test, have a look at the keyboard matrix
In the new board, you should then unsolder the appropriate EMI
filter (next to the control ports) and shortcut it by soldering
in a wire between the two outer pins of the three. If this seems
to work, you can safely operate your C-64 this way.
In the old board (or if removal of the EMI filter did not
help), you could try a pull-up resistor between +5V and the
appropriate CIA pin. Try a value of 5.6k. If this works, try 10k
too, to minimize the CIA output load, if it does not, try 3.3k.
If nothing of the above helps, your CIA is seriously damaged
and must be replaced
Updated: May 18th, 1999
Created: January 1997
Status : NOT VERIFIED!
Site copyright © 1997 by Marc-Jano Knopp
This document is part of MJK's Commodore 64 & LCD Page
Brought back to life by Peter Schepers, Dec 10, 2005 because I really liked this site!